1. Field of the Invention
The present invention relates to a robot hand for gripping and conveying a cylindrical object, and relates to a robot having the robot hand.
2. Description of the Related Art
In the prior art, various devices have been known for gripping and conveying a cylindrical object. For example, JP 2004-345051 A discloses a gripping device having a drive shaft gear 2, three driven gears 3 which engages an outer diameter of drive shaft gear 2 and are equally-spaced in a circumferential direction of gear 2, and a claw 6 extending in an axial direction from an arm 5 which is pivotal about a driven shaft 4 of each driven gear.
JP 2011-083837 A discloses a robot hand configured to grip an inner or outer surface of a workpiece 10 by means of three or more hand claws 14, and insert workpiece 10 into a chuck position of a work chuck device. Further, it is described that the robot hand has a free-rotation mechanism for freely rotating workpiece 10 when external force in a rotational direction about an axis is applied to workpiece 10 gripped by hand claws 14.
Further, JP 2011-157200 A discloses a tire selecting device wherein gripping arms 24a to 24c, respectively having freely-rotating rollers R11 to R13, grip an inner peripheral portion of a tire, and a barcode on the tire is read by rotating the tire.
In a structure wherein a robot hand is rotatably attached to a robot arm via a rotatable wrist shaft, when the robot hand is rotated by a certain angle or more, a cable connected to the hand may become tangled in the wrist shaft and/or excess external force may be applied to the cable. Therefore, in many cases, the rotation angle of the wrist shaft is limited to a certain range. Further, when a means to grip an object and a means to rotate the object are different, although there is no limitation regarding the rotation angle, the entire apparatus may be large, whereby such an apparatus is disadvantageous in terms of cost and operation.